AlGaN Laser Diode Cladding for Low-Loss Carrier Injection
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Solution Overview
Problem
Laser diodes with high Al composition in the AlxGa1-xN mixed-crystal system face challenges in achieving high longitudinal conductivity and low transverse to longitudinal resistivity ratio while minimizing internal loss, particularly due to the composition gradient layer's high transverse to longitudinal resistivity ratio and optical mode absorption into electrodes.
Innovation Solution
The laser diode design includes a p-type cladding layer with a p-type longitudinal conduction layer having a decreasing Al composition gradient and a p-type transverse conduction layer, both formed on an AlN single crystal substrate, to enhance conductivity and reduce internal loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a composition gradient layer with high Al composition is used to improve carrier injection efficiency, then the longitudinal conductivity increases, but the transverse to longitudinal resistivity ratio becomes large
Solution Approach 1:
The p-type cladding layer is divided into multiple sub-layers with different Al compositions (first through fourth sub-layers), each contributing differently to longitudinal and transverse conductivity. This segmentation allows independent optimization of conductivity ratios in different directions, resolving the contradiction between improving carrier injection and maintaining appropriate resistivity ratios.
Solution Approach 2:
Different regions of the p-type cladding layer are assigned different Al compositions tailored to local functional requirements. The first sub-layer near the light-emitting layer has lower Al composition for better transverse conductivity, while higher Al composition regions provide necessary longitudinal conductivity, achieving local optimization of electrical properties.
2Loss of energy
If the Al composition in the cladding layer is increased to reduce internal loss, then optical confinement improves, but optical mode absorption into electrodes increases
Solution Approach 1:
The cladding layer is segmented into multiple sub-layers with progressively varying Al compositions. This gradual transition prevents abrupt refractive index changes that would cause optical mode absorption, while still achieving effective optical confinement through the overall composition gradient, thus reducing internal loss without increasing electrode absorption.
3Ease of manufacture
If a uniform composition layer is used to simplify manufacturing, then fabrication process becomes easier, but carrier injection efficiency decreases
Solution Approach 1:
The cladding layer is fabricated as multiple sub-layers that can be deposited sequentially using standard epitaxial growth techniques. While more layers than a uniform composition, this segmented approach remains compatible with conventional manufacturing processes and enables precise control of carrier injection efficiency through composition grading.
Solution Approach 2:
The Al composition parameter is gradually changed across different sub-layers rather than maintained uniform. This parameter variation is achieved through controlled adjustment of precursor ratios during sequential epitaxial growth, maintaining manufacturing feasibility while dramatically improving carrier injection efficiency.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The design achieves high longitudinal conductivity and low transverse to longitudinal resistivity ratio, effectively suppressing internal loss and improving carrier injection efficiency.
Implementation Method 1
a p-type longitudinal conduction layer that includes AlsGa1-sN (0.3≤s≤1), has a composition gradient such that an Al composition s decreases with increased distance from the substrate
Implementation Method 2
p-type longitudinal conduction layer... has a film thickness of less than 0.5 μm
Implementation Method 3
a p-type transverse conduction layer that includes AltGa1-tN (0≤t<0.3)... has a film thickness of 0.5 μm or more
Implementation Method 4
a light-emitting layer formed on the n-type cladding layer and including one or more quantum wells
Implementation Method 5
By growing AlxGa1-xN mixed crystals on an AlN single crystal substrate, which has been introduced in recent years, a good nitride semiconductor with a reduced defect density can be obtained
Data Source
AI summary
A laser diode (1) includes an AlN single crystal substrate (11), an n-type cladding layer (12) formed on the substrate and including a nitride semiconductor layer having n-type conductivity, a light-emitting layer (14) formed on the n-type cladding layer and including one or more quantum wells, a p-type cladding layer (20) formed on the light-emitting layer and including a nitride semiconductor layer having p-type conductivity, and a p-type contact layer (18) formed on the p-type cladding layer and including a nitride semiconductor that includes GaN. The p-type cladding layer includes a p-type longitudinal conduction layer (16) that includes AlsGa1-sN (0.3≤s≤1), has a composition gradient such that the Al composition s decreases with increased distance from the substrate, and has a film thickness of less than 0.5 μm, and a p-type transverse conduction layer (17) that includes AltGa1-tN (0<t≤1).